There exists within the art apparatus and method for coupling reinforcing bars used in structural concrete, such coupling commonly involves the use of a tubular steel coupling body or sleeve configured to receive end portions of the reinforcing bars. Typically, the bars are held in place using a number of engaging bolts which engage into the surfaces of the bars wedging them against an inner surface of the tubular body thereby providing a couple.
In particular, U.S. Pat. No. 5,046,878, GB 2220241 and EP 0554972 all disclose a reinforcing bar coupling system as detailed with reference to FIG. 1 herein. FIG. 1 herein illustrates a cross-sectional side elevation view of a bar coupling system found in the art comprising an elongate tubular body 102, a plurality of engagers 103, at least one gripping surface 104 and an inner surface 105. According to the prior art coupling device 100, elongate tubular body 102 receives reinforcing bar end portions 101 such that engagers 103 are adjustably positioned through the tubular body 102 and serve to wedge bars 101 against gripping surface 104, gripping surface 104 being wedged, in turn, against inner surface 105, thereby forming a couple.
According to EP 0554972 and with reference to FIG. 3 therein, the gripping surfaces may be formed as adjustably placed ribs extending the length of the tubular body, these ribs being provided with profiles so as to key into both the inner surface of the tubular body and the reinforcing bars. According to an alternative embodiment and with reference to EP 0554972 and FIG. 6 therein, the ribs may be formed integrally with the tubular body and project outwardly from the tubular body inner surface towards the center of the coupling device. According to both embodiments the reinforcing bars are configured to sit on top of the ribs so as to be positioned away from the inner surface of the tubular body.
U.S. Pat. No. 5,664,902, U.S. Pat. No. 5,909,980 and U.S. Pat. No. 6,202,282 disclose an elongate tubular body configured for receiving end portions of reinforcing bars in a similar manner to that described above with reference to FIG. 1 herein and associated prior art. In particular, these latter prior art documents are not concerned with the provision of a gripping surface configured to engage into the reinforcing bars using a plurality of teeth, instead the tubular body is provided with a non-cylindrical inner surface such that the reinforcing bars, following engagement by the engaging bolts are wedged against a portion of the inner surface as detailed with reference to U.S. Pat. No. 6,202,282 and FIGS. 3, 4 and 12 therein. Through the provision of a non-cylindrical inner surface, the reinforcing bars are seated and wedged against discreet regions of the inner surface of the tubular body.
As such, all prior art documents identified above teach of a coupling device being configured to wedge the reinforcing bars against at least one inner surface of the tubular body, the surface(s) being flat or convex with respect to an outer radial surface of the reinforcing bars. Accordingly, the inventors have identified numerous disadvantages associated with such coupling devices found in the art and identified above, these include:                A common problem encountered with prior art coupling devices utilizing non-integrally formed ribs extending the length of the tubular body as illustrated above, is substantial bar slip in response to an applied tensile load. Bar slippage within the coupler body is a result of poor or minimal reinforcing bar—coupler contact. In particular, where the ribs are used as a gripping surface, the bars are susceptible to slip as a result of firstly, points of contact between the adjustably placed ribs and the coupler body and secondly, points of contact between the adjustably placed ribs and the reinforcing bars.        The utilization of gripping ribs, in the form of insertable ribs, within the tubular body necessitates a substantial amount of care be taken when assembling the coupling joint so as to ensure the ribs are not displaced from their mountings (light weld) on the inner surface of the tubular body. The displacement of a rib, within the tubular body, may result from contact between an end portion of a reinforcing bar and the rib at a region where the bar is introduced into the coupler body. If rib displacement does occur then either, the joint needs reassembling or if undetected, the joint is weakened yet further due to the incorrect alignment of the rib(s).        A profiled gripping surface, typically comprising teeth, which is located away from the tubular body inner surface and towards the center of the coupling device requires elaborate manufacture, or assembly in that either sophisticated tooling is required to form the tubular body having integrally formed ribs which project away from the inner surface or non-integrally formed ribs which are added after the formation of the tubular body. In the case where non-integrally formed ribs are provided it is common to observe incorrect positioning of the ribs within the tubular body resulting ultimately in poor rib—reinforcing bar contact, and a corresponding weak joint.        Through the utilization of a flat or convex gripping surface with respect to the radial outer surface of the reinforcing bars, minimal contact is achieved between the coupling device and the reinforcing bars resulting in reduced loading force transfer from the reinforcing bars to the coupling device. Additionally, the absence of teeth on the gripping surface(s), being in reduced contact with the reinforcing bars, does not provide for a strong couple.        As a consequence of this poor reinforcing bar—coupler interaction, at the gripping surface(s), penetration of the bars by the engagers is required so as to increase this interaction. This in turn creates additional disadvantages in that due to the penetration of the engagers into the reinforcing bars, breaking of the bars is experienced within the coupler body in response to a sufficiently high loading force applied laterally to the reinforcing bars.        
The present invention endeavors to address and overcome the above identified disadvantages by providing a coupling device as detailed herein below.